Extension verifier doesn't check for dot. (minor issue)

[leewz]

For example, the Studio accepts "adhoc" as having a valid C extension, because it ends with a "c". Strangely, the C file will be created as "adhoc.c", making the check unnecessary. This is because it's a simple suffix check. ("adhoc.cppc" will also be created as "adhoc.cppc.c".)

The intended check may be:

• If the file DOES have an extension, make sure it's correct.
• If it doesn't, add an extension.

[Rupeshiya]

@leewz So instead of returning error message ,It is expected to return 'filename.c' ??